U.S.-Egyptian scientist Ahmed Zewail once received a medal from President Hosni Mubarak. Now, he says, it's time for the Egyptian leader to heed the demonstrators clamouring for his departure.

He should step down tomorrow and allow for a transitional government, Zewail told Reuters in an interview on Wednesday.

Zewail, 64, who won the Nobel prize for physics in 1999 and was awarded the Grand Collar of the Nile by Mubarak the same year, has long enjoyed a celebrity cachet in his native land.

Despite all his access to the ruling elite, Zewail said, his own efforts over 15 years to promote science, technology and education in Egypt had proved futile against the dead weight of corruption and bureaucracy. Really we didn't get anywhere.

Since he returned to Egypt a week ago, Zewail has met Mubarak's new vice-president, Omar Suleiman, Arab League chief Amr Moussa, the head of al-Azhar, a seat of Islamic learning, and leaders of the youthful protesters occupying Tahrir Square.

He was exploring what a wise man role he might play between regime and revolution, but the rift may be too wide.

I thought in the beginning there might be a middle ground, but I'm not sure any more, he said. In a situation like that, you cannot negotiate. You cannot slow things down.

Comparing Egypt to a diseased body, he recommended swift surgery, not aspirin.

I know exactly what the youth want. They want to see a new Egypt. It's as simple of that, said Zewail, who serves as U.S. President Barack Obama's science envoy to the Middle East.

It's a transformative point, he said of the popular unrest aimed at ending Mubarak's 30 years in power, turbulence that has shaken Egypt and the Arab world. This is a paradigm shift.

WINDOW ON THE WORLD

Zewail said he has no interest in insulting Mubarak or attacking him personally.

It's an attack on the whole system, which was corrupt and not functioning properly. Egypt deserves a new, fresh system, a new window on the world.

He brushed aside arguments about constitutional tangles that could impede a transition to democracy were Mubarak to resign on the spot, saying the right mechanisms could be found.

The question is do we have the will to do it and to do it in a speedy way to end this problem so everybody can go back to work and set the country on a new trajectory.

He declined to assess the sincerity of Suleiman's efforts to manage the transition to a new president, now that Mubarak has promised not to seek another term in a September election, but said simply fixing the old system would not satisfy Egyptians.

The army can play a significant role in this, in protecting the nation in the transition period, he added, praising the way troops had so far avoided shooting at demonstrators.

The people of Egypt will achieve what they want. I just hope it will not require a bloody situation in order to complete the journey. That's the only fear that remains in me, he said.

Zewail counselled the United States and other outside powers to use caution before interfering in what he called a genuine, homegrown, youth-driven revolution.

What the U.S. should do consistently is to support the liberty of the Egyptian people.

Asked if he saw himself as a future presidential candidate, Zewail said the issue was not relevant for now.

The key thing right now is to take the country into a democratic step forward and then to have a real constitution in place and let the Egyptian people surprise us with what they want.

He dismissed the idea that the Muslim Brotherhood might hijack events or that Egypt's 1979 peace treaty with Israel was in peril, saying democracy could only benefit the region.

The outcry against Mubarak's rule is sure to resonate far beyond Egypt's borders, Zewail said.

They always said Egypt is the heart of the Arab world. That heart is beating. The music will have to be listened to somewhere else.

Egypt Israel Nobel prize Barack obama